Any way to use the timeline markers as input list?
First, we should get the frames at which the markers are set, to do this, we can use this list comprehension:

[marker.frame for marker in bpy.context.scene.timeline_markers]


Which returns the frames at which the markers were set:



Next, I am going to subtract the current frame from this list, now all the markers that have frame values less than the current frame will have negative values. If I max the output with zero, all the values that were negative will become zero. If I "not" (Invert) the result, all zeros becomes ones and non zeros becomes zeros. If I sum all the values of the output, I will get the number of markers that are before or at the current frame. I can now use this output in a Trim Text Node to show the characters:



Which results in: